The present invention relates to a metal gasket with a sealing bead and a bead protecting portion, in particular a single metal plate with a compressible sealing bead and a bead protecting portion for protecting the sealing bead. The invention can be applied to gaskets for sealing a narrow area as well as a wide area, such as a pipe connecting gasket and a cylinder head gasket for an internal combustion engine.
The engines have been developed to provide high power with light weight. Since metal gaskets or metal laminate gaskets are strong against high pressure and high temperature, the metal gaskets have been used widely for the engines. To provide high power with light weight engine, the gasket must be made thin, and seal around the cylinder bores tightly.
If the areas around the cylinder bores of the engine are not properly sealed, combustion gases leak from the cylinder bores, so that the maximum power of the engine can not be obtained. In order to properly seal around the cylinder bores, various metal laminate gaskets have been proposed. For example, one or more metal plates have sealing beads around the cylinder bores, and protecting portions for preventing deformation or creep relaxation of the beads are formed near the sealing beads.
For example, a metal laminate gasket as disclosed in Japanese Patent Publication (KOKAI) No. 8-100859 is formed of three metal plates laminated together, wherein upper and lower metal plates have beads around holes to be sealed, and a middle plate thicker than the upper and lower plates includes bead protecting portions, which do not deform when the gasket is compressed. The beads extend toward the middle plate, and the bead protecting portions are located at both sides of each bead. Since the beads are not completely compressed by the bead protecting portions when the gasket is tightened, the beads seal around the holes without creep relaxation.
The above gasket is formed of three plates, or it requires at least two plates, one plate for the bead and the other plate for the bead protecting portion. Since the gasket becomes relatively thick, it is possible to use such a gasket as a large cylinder head gasket, but the gasket is not suitable as a small gasket.
Also, since the above gasket is formed of three metal plates with different functions, the gasket operates as a combination of the three metal plates. Therefore, one of the metal plates can not be selected and used as a single plate gasket because of providing insufficient or improper sealing around the hole.
On the other hand, in some conventional gaskets, an edge portion of a metal plate may be turned over a base of the metal plate to form a seal portion or a bead protecting portion around the edge portion. However, in this gasket, since the bead protecting portion can be formed only at the edge portion of the gasket, the structure of the gasket, i.e. locations of the bead and the bead protecting portion, is limited.
The present invention has been made in view of the above conventional gaskets, and an object of the invention is to provide a metal gasket, which is thin and can securely seal around a hole while protecting a bead by a bead protecting portion.
Another object of the invention is to provide a metal gasket as stated above, wherein a sealing bead and a bead protecting portion for the sealing bead can be formed in desired portions in a metal plate.
A further object of the invention is to provide a metal gasket as stated above, which is suitable for sealing a small area like a pipe connecting gasket as well as a large area like a cylinder head gasket.
Further objects and advantages of the invention will be apparent from the following description of the invention.